JP6041728B2 - Method for producing thin film cubic zirconia sheet for solid oxide fuel cell - Google Patents

Description

The present invention relates to a thin film cubic zirconia sheet for a solid oxide fuel cell, particularly a dense and excellent dimensional accuracy sheet thickness of 50 μm to 160 μm and a planar area of 50 cm ² or more. It is related with the manufacturing method.

  Conventionally, zirconia stabilized with yttria, which is an oxygen ion conductor, has been widely used as a solid electrolyte of a solid oxide fuel cell (hereinafter also referred to as SOFC). In particular, since the electrolyte-supporting cell needs strength to hold the cell by the electrolyte itself, a tetragonal zirconia sheet having excellent strength characteristics is preferable as the solid electrolyte membrane. However, since tetragonal zirconia has lower oxygen ion conductivity than cubic zirconia, cell power generation performance tends to be inferior. On the other hand, since cubic zirconia has inferior strength characteristics to tetragonal zirconia, the cell strength is maintained by increasing the thickness of the cubic zirconia sheet in the electrolyte-supported cell. However, when the electrolyte is thick, there is a problem that the resistance in the electrolyte increases and the cell power generation performance decreases.

  In recent years, cost performance needs to be further improved in order to make SOFC systems versatile, and in order to manufacture electrolyte-supported cells with high power generation performance, the use of cubic zirconia sheets has become thinner, especially handling strength. Therefore, a cubic zirconia sheet having an excellent thickness of 50 μm or more and 160 μm or less is required.

  However, with regard to increasing the strength of the cubic zirconia sheet, there is a study of a method for producing a scandia-stabilized zirconia sheet (Patent Document 1) that reduces the residual pores in the sheet and densifies it to increase the mechanical strength of the electrolyte sheet. However, there has been almost no study on thinning a cubic zirconia sheet with a thickness of 200 μm or less.

JP 2011-204398 A

  Generally, the bending strength of a cubic zirconia sheet is almost 0.3 to 0.4 GPa regardless of the thickness of the sheet when measured according to JIS standard (JIS R1601). The maximum load value when the sheet breaks greatly depends on the thickness of the sheet, and is inversely proportional to the square of the thickness of the sheet. Therefore, in the thin film cubic zirconia sheet having a thickness of 50 μm or more and 160 μm or less, there is a big problem in handling property because it is easy to be easily cracked or chipped even if a slight external force is applied to the sheet.

In particular, when a large thin-film cubic zirconia sheet having a sheet area of 50 cm ² or more is produced, there is a problem that cracks and chips are noticeable in the sheet immediately after firing, and the sheet production yield is lowered. Further, it has been found that there is a problem that the dimensional accuracy in the planar direction of the thin film sheet is lowered, specifically, the difference between the dimensions in the X direction and the Y direction tends to increase.

  The present invention has been made in view of the above circumstances, and it is possible to suppress a decrease in production yield of a thin film cubic zirconia sheet having a high density (relative density of 99% or more) and a thickness of 50 μm to 160 μm, and high dimensional accuracy. An object of the present invention is to provide a method for producing a thin film cubic zirconia sheet for SOFC.

  The present inventor further researched the relationship between the physical properties of powders and slurries used as raw materials and the resulting sheet cracking and chipping occurrence rate for the method for producing a thin film cubic zirconia sheet. As a result, the specific surface area of the raw material cubic stabilized zirconia powder and the proportion of coarse particles in the powder are further reduced from the viewpoint of increasing the powder filling rate in the green sheet and reducing the firing shrinkage rate. As a result, it was found that the production yield of the thin film cubic zirconia sheet excellent in handling strength could be suppressed, and the present invention was completed.

A method for producing a thin film cubic zirconia sheet for a solid oxide fuel cell having a thickness of 50 μm or more and 160 μm or less according to the present invention, which has been able to solve the above problems, comprises cubic stabilized zirconia powder, solvent and binder A step of preparing a slurry by mixing slurry raw materials containing a slurry; a step of continuously coating a polymer film on a polymer film by a tape casting method using the obtained slurry and drying to obtain a green tape; A step of punching and cutting the obtained green tape into a predetermined shape to obtain a green sheet; a step of firing the obtained green sheet; and a BET specific surface area of the zirconia powder of 3 m ² / g or more and 10 m ² / g or less , and the and the 90% by volume diameter of the zirconia powder _{(D 90)} is at 0.25μm or 0.8μm or less, 50% by volume _{(D 50)} and the ratio of 90 volume% diameter _(D 90 _/ D ₅₀₎ is 2 or less than 1, the ratio of 90 volume% diameter _{(D 90)} and 100 volume% diameter _{(D 100) (D 100} / D ₉₀ ) is characterized by using a powder having a value of more than 1 and 4 or less.

  By using the cubic stabilized zirconia powder as a raw material powder, the specific surface area of the powder is small, and the content of coarse particles (particles of about 1.0 μm or more) in the powder is very small and the average particle Since the diameter is small and the particle size distribution is sharp, the amount of binder necessary for forming the green tape can be reduced, and the powder filling rate in the green tape can be increased. As a result, the firing shrinkage rate of the green sheet is reduced, so that external force and stress are less likely to be applied to the sheet being fired, and the generation of cracks and chips in the thin-film cubic zirconia sheet immediately after firing is reduced. As a result, a high yield can be maintained.

  Furthermore, the dimensional shrinkage in the X direction and the Y direction when the green sheet is fired is stabilized, and the difference between the dimensions in the X direction and the Y direction becomes very small, so that a thin film electrolyte sheet having high dimensional accuracy can be obtained. Became.

Moreover, it is also a preferable aspect to use a powder having a bulk density of 1.05 g / cm ³ or more and 1.3 g / cm ³ or less as the cubic stabilized zirconia powder. In this case, the amount of binder to be used is further reduced, and a thin film electrolyte sheet having higher dimensional accuracy can be obtained.

  Furthermore, it is also a preferred embodiment that a recovered green body containing cubic stabilized zirconia powder is used as the slurry raw material. In this case, the amount of the recovered green body used is converted to the mass of the cubic stabilized zirconia powder contained in the recovered green body, and 5% of the total cubic stabilized zirconia powder contained in the slurry. It is preferable to set it as the mass% or more and 50 mass parts or less.

  Moreover, by making the solid content concentration of the slurry in the range of 70 to 90% by mass, it is possible to easily increase the powder filling rate in the green tape and maintain a higher yield.

  According to the present invention, it is possible to obtain a thin film cubic zirconia sheet for SOFC that can suppress a decrease in sheet manufacturing yield and has high dimensional accuracy.

  The method for producing a thin-film scandiazirconia sheet for a solid oxide fuel cell according to the present invention comprises a step of preparing a slurry by mixing a slurry raw material containing cubic stabilized zirconia powder, a solvent and a binder; Using a tape casting method to continuously apply a tape on a polymer film and drying it to make a green tape; punching and cutting the resulting green tape into a predetermined shape to make a green sheet : Firing the obtained green sheet. Hereinafter, each of these steps will be described in detail.

1. First, the process of adjusting the slurry will be described. In this step, cubic stabilized zirconia powder, a solvent, a binder, and, if necessary, a plasticizer and a dispersant are mixed by a ball mill or a bead mill to prepare a slurry.

The cubic stabilized zirconia powder has a BET specific surface area of 3 m ² / g or more and 10 m ² / g or less, and a 90 volume% diameter (D ₉₀ ) of 0.25 μm or more and 0.8 μm or less. The ratio between the volume% diameter (D ₅₀ ) and the 90 volume% diameter (D ₉₀ / D ₅₀ ) is more than 1 and 2 or less, and the ratio between the 90 volume% diameter (D ₉₀ ) and the 100 volume% diameter (D ₁₀₀ ) ( A powder having D ₁₀₀ / D ₉₀ ) of more than 1 and 4 or less is used.

  The cubic stabilized zirconia powder is a zirconia powder mainly composed of cubic crystals in the intensity of diffraction peaks obtained by a powder X-ray diffraction method. Specifically, each peak intensity is obtained from the X-ray diffraction pattern of the zirconia crystal in the zirconia powder, a cubic ratio (%) is obtained from each intensity value and the following formula, and the cubic ratio is 80% or more. Preferably, it is 90% or more, more preferably 95% or more. The reason why the cubic crystal ratio is set to 80% or more is that if it is less than 80%, the oxygen ion conductivity and bending strength of the obtained zirconia sheet tend to be impaired.

Cubic crystal ratio (%) = (100−monoclinic crystal ratio) * (c (400)) ÷ (t (400) + t (004) + c (400)).
Monoclinic crystal ratio (%) = (m (111) + m (−111)) ÷ (m (111) + m (−111) + tc (111)) * 100
(Where c (400) indicates the peak intensity of the cubic (400) plane, t (400) and t (004) indicate the peak intensity of the tetragonal (400) plane and (004) plane, and m ( 111) and m (−111) indicate the peak intensities of the monoclinic (111) plane and the (−111) plane, and tc (111) indicates the peak intensity of the (111) plane of the superimposed tetragonal and cubic crystals. Show.)
The cubic stabilized zirconia powder having the crystal structure is Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ as a stabilizer. , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Yb ₂ O _{3 and} other rare earth metal oxides; MgO, CaO, SrO, BaO, etc. In particular, a stabilized zirconia containing 7 to 15 mol% of an oxide of at least one element selected from the group consisting of scandium, yttrium, cerium, and ytterbium is preferable.

  Among these, in the case of a scandia-stabilized zirconia (hereinafter sometimes referred to as “ScSZ”) powder, the content of scandia is 7 to 12 mol%, preferably 8 to 11 mol%. In the case of powdered zirconia (hereinafter sometimes referred to as “ScCeSZ”), the content of scandia and ceria is 7 to 12 mol% scandia 0.5 to 3 mol% ceria, preferably 8 to 11 mol% scandia. , Ceria 1-2 mol%.

In the case of yttria-stabilized zirconia (hereinafter sometimes referred to as “YSZ”) powder, the yttria content is 7 to 12 mol%, preferably 8 to 10 mol%. In the case of powder, the ytterbia content is 8 to 15 mol%, preferably 9 to 12 mol%. In addition, it is also possible to add 0.03 to ₃ mol% of Al ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , TiO ₂ , Bi ₂ O ₃ , In ₂ O _{3 and the} like together with these stabilizers. is there.

The cubic stabilized zirconia powder has a BET specific surface area of 3 m ² / g or more, preferably 4 m ² / g or more, more preferably 5 m ² / g or more. Moreover, it is 10 m < ² > / g or less, Preferably it is 8 m < ² > / g or less, More preferably, it is 7 m < ² > / g or less. If the BET specific surface area is in the above range, the necessary amount of binder for forming the green tape is reduced, so that the residual pores in the cubic zirconia sheet obtained by increasing the powder filling rate in the green sheet are further increased. By reducing the density, a dense sheet having a relative density of 99% or more can be obtained.

The cubic volume zirconia powder has a 90 volume% diameter (D ₉₀ ) of 0.25 μm or more and 0.8 μm or less. If D ₉₀ of greater than 0.8 [mu] m, the aggregate of the zirconia powder is increased since the powder packing ratio is reduced, the strength of the resulting thin film zirconia sheet is lowered. If it is less than D ₉₀ of 0.25 [mu] m, since the fine nano-sized particles is increased in the zirconia powder, so that the amount of the binder is impaired dimensional accuracy becomes more necessary for reverse. The D ₉₀ is more preferably 0.26 μm or more, further preferably 0.27 μm or more, particularly preferably 0.28 μm or more, more preferably 0.7 μm or less, still more preferably 0.65 μm or less, particularly preferably 0. .6 μm or less.

Further, the ratio (D ₉₀ / D ₅₀ ) of 50 volume% diameter and 90 volume% diameter of the cubic zirconia powder is more than 1 and 2 or less. If the ratio (D ₉₀ / D ₅₀ ) is within the above range, the amount of binder required for green sheet molding can be further reduced, the firing shrinkage ratio is lowered, and cracking and chipping of the zirconia sheet after firing are reduced. Yield is improved. The ratio (D ₉₀ / D ₅₀ ) is more preferably 1.05 or more, further preferably 1.1 or more, more preferably 1.9 or less, and still more preferably 1.8 or less.

Furthermore, the ratio (D ₁₀₀ / D ₉₀ ) of 90 volume% diameter and 100 volume% diameter of the cubic zirconia powder is more than 1 and 4 or less. If the ratio (D ₁₀₀ / D ₉₀ ) is within the above range, the ratio of extremely coarse particles is reduced, and the powder filling rate in the green sheet can be further increased, and the sheet bending strength is also enhanced. Tend to be. The ratio (D ₁₀₀ / D ₉₀ ) is more preferably 1.2 or more, further preferably 1.5 or more, more preferably 3.5 or less, still more preferably 3.0 or less, and particularly preferably 2. 5 or less.

  In the present invention, the 50 volume% diameter is measured by a laser diffraction / scattering particle size distribution measuring apparatus (trade name “LA-920”, manufactured by Horiba, Ltd.), and the particle volume is integrated from the smaller particle diameter. The particle diameter is 50% by volume with respect to the total particle volume. Similarly, the 90 volume% diameter and the 100 volume% diameter are values of the particle diameter that are 90 volume% or 100 volume% with respect to the total particle volume by integrating the particle volume from the smaller particle diameter.

  In addition, since the cubic stabilized zirconia powder used in the present invention is hardly a commercially available cubic stabilized zirconia powder, the commercially available cubic stabilized zirconia powder is used at 1000 to 1400 ° C. A method of pulverizing the heat-treated product, a method of mixing a commercially available zirconia powder and the stabilizer powder, a method of pulverizing the heat-treated product, a cubic stabilized zirconia powder or the mixed powder, and then calcining or sintering It can obtain by the method etc. which grind | pulverize and grind | pulverize the baked body obtained by heat-processing by the above.

  Since the pore volume and pore diameter in the cubic stabilized zirconia powder are reduced by heat treatment, calcining or sintering, the specific surface area is lowered and the amount of binder for tape molding is reduced. In order to improve the reproducibility of the particle size distribution such as D90 of the powder obtained in the pulverizing step, it is preferable to use a cubic stabilized zirconia powder, which suppresses the aggregation and sintering of the powder and has a desired particle size. It is preferable that the powder is uniformly heat-treated in the above temperature range while flowing in a rotary kiln so that the powder can be easily pulverized.

Further, by pulverizing the heat-treated powder or fired body, the ratios of D ₉₀ , D ₉₀ / D ₅₀ and D ₁₀₀ / D _{90 of} the present invention are adjusted. In order to adjust the particle size distribution of the raw material zirconia powder to a specific range as described above, pulverization is performed using a ball mill, a bead mill, a planetary mill, a jet mill, or the like.

  Since the material to be crushed is a heat-treated, calcined or sintered powder or fired body, it is harder than the commercially available cubic stabilized zirconia powder, and the input (grinding) power and peripheral speed are increased. If a strong shearing force is applied, re-aggregation or an abnormal increase in viscosity may occur in an overdispersed state where even the primary particles of the powder are broken. Therefore, it is preferable to grind efficiently and mildly without overdispersing, and for that purpose, using a circulating wet bead mill, zirconia beads having a particle diameter of 0.05 to 3 mmφ as a grinding medium, water or as a dispersion medium Using lower alcohol such as ethanol or isopropanol, the mixture is pulverized under the conditions of stirring power of 0.5 to 5 kWh / kg and peripheral speed of 6 to 12 m / s. More preferably, the stirring power is 0.6 to 1.5 kWh / kg and the peripheral speed is 7 to 10 m / s.

  Further, a dispersant may be added as necessary, and when the material to be pulverized is a very hard sintered body, it is preferable to pre-grind dry, wet, or a combination of dry and wet.

  To the slurry raw material powder, ceramic powder made of alumina, titania, silica, niobium oxide, thallium oxide or the like may be added in addition to the cubic stabilized zirconia powder to the extent that the effects of the present invention are not impaired. The amount of the ceramic powder used is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 3% by mass or less with respect to the total of the raw material powders.

  The kind in particular of binder used for a slurry is not restrict | limited, A conventionally well-known organic binder can be selected suitably and can be used. Examples of organic binders include ethylene copolymers, styrene copolymers, (meth) acrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, and vinyl acetal resins. And vinyl formal resins, vinyl alcohol resins, waxes, celluloses such as ethyl cellulose, and the like.

  Among these, from the viewpoint of suppressing the moldability, punching processability, strength, and shrinkage ratio variation during firing of the zirconia green sheet, it is thermoplastic and has a number average molecular weight of 20000 to 250,000, more preferably 50000 to 200000 (meta ) Acrylate copolymers are recommended as preferred.

  The amount of the binder used varies depending on the particle size and particle size distribution of the cubic zirconia powder in the raw material and / or slurry, but is preferably 5 parts by mass or more, more preferably 7 parts by mass or more with respect to 100 parts by mass of the raw material powder. More preferably, it is 8 mass parts or more, 16 mass parts or less are preferable, More preferably, it is 15 mass parts or less, More preferably, it is 14 mass parts or less.

  If the amount of the binder used is insufficient, the moldability of the zirconia green sheet is lowered, and the strength and flexibility may be insufficient. On the other hand, if the amount is too large, not only will it be difficult to adjust the viscosity of the slurry, but the decomposition and release of the binder component during degreasing / sintering will increase and become violent, resulting in large variations in linear shrinkage in the X and Y directions. , Dimensional stability can be reduced.

  Solvents for slurry include water; alcohols such as methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane and heptane Aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and acetates such as methyl acetate, ethyl acetate, and butyl acetate, and the like.

  These solvents can be used alone or in combination of two or more. The amount of these solvents to be used is preferably adjusted in consideration of the viscosity of the slurry at the time of forming the zirconia green sheet. A suitable slurry viscosity is 1 Pa · s or more and 50 Pa · s or less, and more preferably 2 Pa · s or more and 20 Pa · s or less.

  Moreover, it is preferable that the solid content density | concentration of a slurry is adjusted to the range of 60-90 mass%. By adjusting the solid content concentration within the above range, the amount of solvent in the green tape during coating can be reduced, and the powder packing density of the green tape can be increased. The solid content concentration referred to in the present invention is represented by the following formula.

Solid content concentration (%) = (mass of zirconia powder + mass of binder solid) / mass of total composition * 100
.... Formula 3
The solid content concentration of the slurry is preferably 70% by mass or more, more preferably 75% by mass, and particularly preferably 80% by mass or more. In addition, when solid content concentration exceeds 90 mass%, slurry viscosity exceeds 50 Pa * s, the fluidity | liquidity of a slurry is impaired and uniform coating to a polymer film becomes difficult.

  In preparing the slurry, it is preferable to use a dispersant in order to promote dispersion of the zirconia raw material powder. Dispersants include polyelectrolytes such as polyacrylic acid and ammonium polyacrylate; partial esters of α-olefin / maleic anhydride copolymers; organic acids such as citric acid and tartaric acid; isobutylene or styrene and maleic anhydride And a copolymer of butadiene and maleic anhydride and an ammonium salt thereof.

  Moreover, it is preferable to add a plasticizer in order to improve the moldability of the slurry. Examples of plasticizers include phthalates such as dibutyl phthalate and dioctyl phthalate; glycols such as propylene glycol and glycol ethers; polyesters such as phthalic polyester, adipic acid polyester, and sebacic acid polyester. be able to. Furthermore, a surfactant, an antifoaming agent, etc. can be added as needed.

  Moreover, in the manufacturing method of this invention, it is also a preferable aspect to use the collection body green body containing the stabilized zirconia powder as a slurry raw material. Since the cubic stabilized zirconia powder is expensive, it is indispensable to use the recovered green body in the actual manufacturing process in order to reduce the cost of the raw material.

  By the way, the stabilized zirconia powder in the green tape by the manufacturing method of the present application has a low content of submicron-class fine particles in the slurry as compared with the case of using a conventional raw material, and is excellent in re-solubility in a solvent. Yes. That is, it can be dissolved to the particle size of the original slurry even in a short time, and agglomerates are hardly generated. Therefore, the generation of pores due to the remaining minute agglomeration can be reduced as compared with the use of the recovered green tape using the conventional raw material.

  Here, the recovered green body containing the stabilized zirconia powder is a green tape and a green sheet that have not been subjected to the firing step. Specifically, after preparing a slurry using the above-mentioned raw material powder, binder, solvent, etc., the tip of the green tape at the beginning of coating that does not have a predetermined coating thickness when producing a green tape using the slurry Part, green tape rear end near the end of coating and left and right ends of green tape; cut waste not used as a green sheet for firing in the case of forming the green tape produced by punching or the like; It is collected. In actual use, a material that is finely divided by a cutting machine, a cutter, or the like, and preferably crushed to 3 cm square or less is used.

  The amount of the recovered green body used is preferably 5% by mass or more in the total stabilized zirconia powder contained in the slurry in terms of the mass of the stabilized zirconia powder contained in the recovered green body, and more preferably. Is 10% by mass or more, more preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less.

  The slurry is prepared by mixing appropriate amounts of the above components. At that time, in order to make each particle finer and to make the particle diameter uniform, the particles may be mixed while being pulverized by a ball mill or a bead mill. Moreover, the order of addition of each component is not particularly limited, and may be according to a conventional method.

2. Production of Green Sheet Next, a process for producing a green sheet using the slurry obtained above will be described. In the production method of the present invention, the obtained slurry is continuously coated on a polymer film in a tape shape by a tape casting method, and dried to obtain a green tape.

  Here, the tape casting method is a method in which a slurry containing raw material powder is applied in a sheet form, and examples thereof include a doctor blade method. In the doctor blade method, in general, a raw material slurry is supplied into a slurry tank, pressure is applied to the slurry, and the slurry is transported to a coating dam via a pipe. It coats on a polymer film so that it may become. The material of the polymer film is not particularly limited, and a conventionally known plastic film can be used. The polymer film is required to have not only flexibility but also sufficient rigidity and strength as a support for the green tape. Therefore, it is preferable to use a PET film having a thickness of 50 μm to 130 μm made of polyethylene terephthalate.

  Thereafter, the slurry coated on the carrier film is dried to obtain a tape-shaped molded product, that is, a green tape. Drying conditions are not particularly limited, and for example, drying may be performed at a constant temperature of room temperature to 150 ° C., or heating may be performed by successively raising the temperature in the order of 50 ° C., 80 ° C., and 120 ° C.

Next, the obtained green tape is punched and cut into a predetermined shape to obtain a green sheet. The shape of the green sheet after punching / cutting may be any of a circle, an ellipse, a square, a square with R (R), etc., and these sheets have the same circle, ellipse, square, and R. It may have one or two or more holes such as squares. The green sheet thickness is 60 μm or more, more preferably 80 μm or more, further preferably 100 μm or more, and is adjusted to a range of 200 μm or less, more preferably 170 μm or less, and further preferably 140 μm or less. Further, the planar area is 60 cm ² or more, more preferably 90 cm ² or more, further preferably 120 cm ² or more, and is adjusted to a range of 600 cm ² or less, more preferably 500 cm ² or less, and further preferably 400 cm ² or less.

  The surface roughness of the zirconia green sheet depends on the raw material-stabilized zirconia powder used, the particle size distribution of the slurry, and the like, but in the case of tape casting by the doctor blade method, it can be adjusted relatively easily as necessary. For example, the slurry may be applied to a roughened PET film, or a roughening sheet or mold having a roughened surface may be pressed onto the green sheet after coating. In general, the surface roughness of the thin film cubic zirconia green sheet for SOFC is preferably in the range of 0.05 μm or more and 1 μm or less in terms of Ra.

The powder filling rate of the green sheet was calculated according to the following procedure. The green sheet mass (W ₁ ) and the green sheet underwater mass (W ₂ ) are measured at room temperature, and the green sheet volume (V ₁ ) is calculated from the water density (ρ _W ).
V ₁ = (W ₁ −W ₂ ) * (ρ _W )... Formula 4
I asked more.

Next, the green sheet was fired in air at 800 ° C. for 1 hour to remove organic components such as a binder in the green sheet, and then cooled to room temperature, and the mass (W ₃ ) after firing was measured. The density (ρ _Z ) of the zirconia sheet is determined by the Archimedes method, and the powder filling rate (PD)
PD = (W ₃ / ρ _Z ) / V ₁ * 100... Formula 5
More calculated.

3. Firing of the green sheet In the step of firing the green sheet, the green sheet produced as described above is fired to obtain a thin film cubic zirconia sheet.

  The method for firing the green sheet is not particularly limited, and a conventionally known method can be employed. For example, it is possible to place green sheets one by one on a shelf and fire them, but for mass production, a stack of green sheets and porous spacer sheets stacked alternately is placed on the shelf. And sintering.

  The structure of a laminated body consists of placing a spacer sheet on the lowest level, stacking green sheets and spacer sheets alternately thereon, and placing a spacer sheet on the uppermost level. The lowermost spacer sheet prevents the green sheet and the shelf board from being joined, and the uppermost spacer sheet serves as a weight to reduce sheet warpage and undulation.

  Specific firing conditions are not particularly limited, and may be based on a conventional method. For example, in order to remove organic components, such as a binder and a plasticizer, from a green sheet, it processes at 100 to 400 degreeC, Preferably it is 150 to 300 degreeC for about 2 hours-50 hours. Next, the zirconia green sheet may be sintered by holding and firing at 1300 ° C. to 1600 ° C., preferably 1350 ° C. to 1550 ° C. for 2 hours to 10 hours.

  At this time, when the green sheet is, for example, a square or a circle, the dimensions of the X direction and the Y direction of the green sheet (in the case of a circle, any one direction is the X direction and the direction perpendicular to the X direction is the Y direction). And, the measured dimensional difference (difference in firing shrinkage) between the X direction and the fired direction after firing is suppressed to 1% or less because of the high powder filling rate in the green sheet, and preferably 0.95% or less. More preferably, it is 0.9% or less.

The thickness and size of the cubic zirconia sheet produced by the production method of the present invention may be adjusted as appropriate. For example, the thickness is 50 μm or more, more preferably 70 μm or more, further preferably 80 μm or more, 160 μm or less, more preferably 140 μm or less, and further preferably 120 μm or less. Further, a zirconia sheet having a planar area of 50 cm ² or more, more preferably 70 cm ² or more, 500 cm ² or less, more preferably 300 cm ² or less, and further preferably 200 cm ² or less can be produced. In addition, the thickness of the said sheet | seat measured 10 arbitrary places about 10 test sheets with a micrometer, the average value was computed, and it was set as sheet | seat thickness.

  In addition, the thin film cubic zirconia sheet produced by the method of the present invention is a dense body having a relative density (density measured by Archimedes method / theoretical density) of 99% or more, and dimensions in the X direction and the Y direction. The difference is very small and the dimensional accuracy is excellent.

Specifically, when the zirconia sheet is square or circular, the dimensional difference ratio (L) between the length in the sheet X direction (L _X ) and the length in the sheet Y direction (L _Y ) is (L _X ) ≧ (L _Y )in the case of,
L = ((L _X ) − (L _Y )) * 100 / (L _X ) / 100... Formula 6
And is in the range of 0% to 1.5%. Preferably it is 1.0% or less, More preferably, it is 0.09% or less, More preferably, it is 0.08% or less, Most preferably, it is 0.07% or less.

  The thin film cubic zirconia sheet is a zirconia sheet whose crystal system is mainly composed of cubic crystals. Specifically, the cubic ratio is 90% or more of the intensity of the diffraction peak of the sheet obtained by the X-ray diffraction method, which is preferable from the viewpoint of high oxygen ion conductivity and bending strength. In addition to cubic crystals, there are diffraction peaks due to monoclinic, tetragonal and rhombohedral crystals, but monoclinic and rhombohedral crystals tend to reduce oxygen ion conductivity and bending strength. Since there is a tendency to reduce oxygen ion conductivity, the cubic ratio is more preferably 95% or more, and particularly preferably 98% or more.

As described above, the thin film cubic zirconia sheet obtained by the production method of the present invention has a thickness of 50 μm or more and 160 μm or less, and is a dense body having excellent dimensional accuracy and handling even when the plane area is 50 cm ² or more. Since it is excellent in strength, it is useful as an electrolyte sheet for SOFC, and the SOFC can efficiently generate power and has a long life.

  In order to obtain an electrolyte-supported cell for SOFC using the cubic zirconia sheet produced by the production method of the present invention as an electrolyte, a conventional method can be used. That is, a fuel electrode is formed on one surface of the zirconia sheet, an air electrode is formed on the other surface, and, if necessary, in order to prevent a reaction between the electrolyte material and the fuel electrode material or the air electrode material, An intermediate layer is formed on one or both sides. Therefore, in order to increase the bonding strength between the electrolyte sheet and the fuel electrode, air electrode or intermediate layer and prevent peeling from the electrolyte, it is preferable to provide the surface of the electrolyte sheet with a surface roughness that provides an anchor effect.

  As the fuel electrode material, generally, cermets of Ni, Co, Ru, etc., stabilized zirconia, and ceria oxide are preferably used. Particularly preferred is a cermet comprising Ni and 9 to 12 mol% scandia-stabilized zirconia. These fuel electrode materials are kneaded with a binder such as ethyl cellulose and a solvent such as α-terpineol to form a fuel electrode paste, or milled to form a fuel electrode slurry, which is coated and dried by a screen printing method, a coating method, or the like. -A fuel electrode can be formed by baking.

As an air electrode material, a perovskite structure oxide having a basic structure of LaMnO ₃ , LaCoO ₃ or LaFeO ₃ , and a mixture obtained by adding stabilized zirconia and / or ceria oxide to these perovskite structure oxides are used. Can be mentioned. Particularly preferably, a mixture obtained by adding 9 to 12 mol% ScSZ to La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ or LaNi _0.6 Fe _0.4 O ₃ is suitably used. . As in the case of the above fuel electrode, an air electrode paste or air electrode slurry is prepared, and the surface of the electrolyte sheet opposite to the fuel electrode is coated, dried, and fired by screen printing, coating, or the like. Can be formed.

  The order of formation of the fuel electrode and the air electrode is not particularly limited. Further, an intermediate layer made of the above ceria oxide may be formed between the solid electrolyte and the air electrode in order to prevent these solid phase reactions. Furthermore, a fuel electrode contact layer may be formed on the fuel electrode, and an air electrode contact layer may be formed on the air electrode.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

1. Evaluation method 1-1. Measurement of specific surface area Using nitrogen as an adsorbed molecule, the specific surface area of the powder was measured by the BET method. As a measuring instrument, a Macsorb HM-1210 type manufactured by Mountec Co., Ltd. was used. The measurement was performed at three points per sample, and the average value was taken as the specific surface area.
1-2. Particle size measurement of raw material powder Using a laser diffraction / scattering particle size distribution measuring device “LA-920” manufactured by HORIBA, Ltd., an aqueous solution in which 0.2% by mass of sodium metaphosphate was added as a dispersant in distilled water was used as a dispersion medium. . The powder was added in an amount of 0.01 to 0.5% by mass in about 100 cm ^{3 of the} dispersion medium and dispersed by sonication for 3 minutes, and then the volume-based particle size distribution was measured.

2. Preparation test examples 1 to 4 of cubic stabilized zirconia powder
A commercially available 8 mol% YSZ powder (manufactured by Daiichi rare element chemical industry, trade name “HSY-8”, specific surface area: 9 m ² / g, D ₅₀ : 0.48 μm, cubic system ratio: 88%) It heat-processed at each temperature of 1050 degreeC, 1200 degreeC, 1300 degreeC, and 1380 degreeC using the rotary kiln whose tube material is an alumina.

  Using a wet-medium circulating bead mill (manufactured by Ashizawa Finetech Co., Ltd.) dedicated to nanoparticle dispersion, 4 kg of the heat-treated YSZ powder and 6 kg of pure water as a dispersion medium were charged as a raw material powder slurry. Here, 4 kg of 0.5 mm-diameter zirconia media (specific gravity: 6) was charged as the grinding media.

The power of the mill motor was adjusted, and the mixture was pulverized in the range of stirring power of 0.5 to 2 kWh / kg and stirring blade tip peripheral speed (ω) of 8 to 10 m / second. The slurry obtained by this wet pulverization was placed in a 10 liter rotary evaporator, and an equal amount of octanol was added to the slurry, and water was distilled off while heating under reduced pressure to obtain an octanol-substituted slurry. The slurry was further heated under reduced pressure to distill octanol and dried under reduced pressure to obtain cubic YSZ powders A ₁₀₅₀ , A ₁₂₀₀ , A ₁₃₀₀ , and A _1380. Table 1 shows the physical properties of each powder. It was.

Test Examples 5-6
10Sc1CeSZ powder stabilized by commercially available 10% by mole scandia 1% by weight ceria (manufactured by Daiichi Rare Element Chemical Co., Ltd., trade name “10Sc1CeSZ”, specific surface area: 11 m ² / g, D ₅₀ : 0.6 μm, D ₉₀ : 1.27 μm, cubic system ratio: 97%) is heat treated at a temperature of 1250 ° C. using a rotary kiln whose core material is alumina, and is crushed and dried in the same manner as in Test Examples 1 to 4 above. Stabilized ScCeSZ powder B ₁₂₅₀ was prepared. In addition, the above-mentioned ScCeSZ powder that has not been heat-treated is pulverized and dried in the same manner as described above using a high-efficiency wet pulverizer (manufactured by Kotobuki Giken Kogyo Co., Ltd., trade name: Apex Mill, model: AMV-1). was prepared ScCeSZ powder _{B NC} stabilized with cubic. The physical properties of these powders are shown in Table 1.

3. Manufacture of cubic zirconia sheet 3.1 Test example 1-6 of green sheet manufacture
100 parts by mass of the powders A ₁₀₅₀ , A ₁₂₀₀ , A ₁₃₀₀ , A ₁₃₈₀ , B ₁₂₅₀ , and B _NC obtained above as raw material powders, 60 parts by mass of toluene as a solvent, and a sorbitan fatty acid ester-based interface as a dispersant A mixture consisting of 1.5 parts by weight of the activator was mixed while being pulverized by a ball mill. To the mixture, a methacrylate copolymer (number average molecular weight: 55000, glass transition temperature: −8 ° C., solid content concentration: 50 mass%) as a binder is 12 to 18 mass parts in solid content concentration, and dibutyl phthalate as a plasticizer. 2 parts by mass was added and mixed with a ball mill for 20 hours to form a slurry. By concentrating and defoaming the obtained slurry, the viscosity at 25 ° C. was adjusted to 2 to 13 Pa · s to obtain a coating slurry.

Each of the above coating slurries was coated on a PET film by a doctor blade method. The PET film was passed through a dryer having three temperature ranges of 50 ° C., 80 ° C., and 110 ° C. at a speed of 0.2 m / min, and then cut with a slitter. The width was 150 mm, the length was 200 m, A long green tape having a thickness of about 105 to 150 μm was obtained. The long green tape was cut to obtain 2000 circular square green sheets GA ₁₀₅₀ , GA ₁₂₀₀ , GA ₁₃₀₀ , GA ₁₃₈₀ , GB ₁₂₅₀ and GB _NC each having a diameter of about 117 to 127 mm.

In addition, in GA ₁₃₀₀ and GB ₁₂₅₀ , in terms of the mass of the stabilized zirconia powder contained in the recovered green tape such as cutting waste, it is 15% and 20% in the total stabilized zirconia powder contained in the slurry. The recovered green body was used. The powder filling rate of each green sheet was measured, and the results are shown in Table 1.

3.2 Reference examples 1 to 3 of green sheet production
With Powder _{A 1050, A 1200, B 1250} , B NC obtained above as raw material powder, except that the thickness was obtained a long green tape about 280μm~340μm in the same manner, a diameter of about 117μm~127mm 2000 circular square green sheets GA ′ ₁₀₅₀ , GA ′ ₁₂₀₀ , GB ′ ₁₂₅₀ and GB ′ _NC were obtained. Incidentally, GA _'1050, GA' ₁₂₀₀ and GB _'NC in recovering the green body is not used, GB' in terms of the weight of the stabilized zirconia powder for _1250, the total stabilized zirconia powder contained in the slurry 20 The recovered green body was used so that the ratio was%. The powder filling rate of each green sheet was measured, and the results are shown in Table 2.

3.3 Green Sheet Firing Test Examples 1-6 and Reference Examples 1-4
Two sheets of rectangular alumina porous sheets (porosity: 45%, thickness: 0.2 mm) having a side of 150 mm are stacked, and the green sheets prepared in Test Examples 1 to 6 and Reference Examples 1 to 4 are stacked thereon. One sheet was stacked, a porous sheet was stacked thereon as a spacer, and 9 sheets of green sheets and porous sheets were alternately stacked to form a laminate.

Four sets of this laminate are placed on a baking shelf (thickness 20 mm, 400 mm × 400 mm), and a mullite / alumina weight jig (porosity: 60%) is placed on the top of each laminate. , Bulk specific gravity: 1.3). By sintering at 1420 ° C. for 3 hours in an air atmosphere, cubic zirconia sheets SA ₁₀₅₀ , SA ₁₂₀₀ , SA ₁₃₀₀ , SA ₁₃₈₀ , SB ₁₂₅₀ , and SB _NC each having a diameter of 100 mm and a thickness of 82 to 126 μm are obtained. A sheet was manufactured.

Further, 1800 cubic zirconia sheets SA ′ ₁₀₅₀ , SA ′ ₁₂₀₀ , SB ′ ₁₂₅₀ and GB ′ _NC each having a diameter of 100 mm and a thickness of 239 μm to 303 μm were manufactured. After cooling, the laminate was disassembled, and cracks and chips of the zirconia sheet immediately after firing were visually observed to determine the rate of occurrence. Further, any 10 out of the above 1800 cubic zirconia sheets are selected, any one direction of the circular sheet is defined as the X direction, the direction perpendicular to the X direction is defined as the Y direction, and the X direction and the Y direction. The dimensions in the direction were measured with calipers, the respective average values were determined, and the ratio of the dimension difference between the X direction and the Y direction with respect to the dimension in the X direction was calculated as the dimension difference rate. The results are shown in Tables 1 and 2.

3.4 Physical Properties of Zirconia Sheet Further, the density of the above nine sheets was measured by the Archimedes method, and the relative density was calculated from the theoretical density of 8YSZ and 10Sc1CeSZ. Further, the cubic ratio was calculated from each peak intensity of X-ray diffraction. The results are shown in Table 1 and Table 2.

  From Table 1, the thin-film cubic zirconia sheets of Test Examples 2, 3, and 5 according to the production method of the present invention have a crack / chip generation rate of 12% or less immediately after firing, and a stable production yield even in a thin film. I understand that. Further, the dimensional difference rate in the XY directions is 1% or less and the relative density is 99% or more, and the sheet is obtained with high density and dimensional stability.

On the other hand, in the production method of the present invention, when the BET specific surface area, D ₉₀ , D ₉₀ / D ₅₀ or D ₁₀₀ / D _{90 of} the zirconia powder used does not satisfy a specific range (Test Examples 1 and 4), a green sheet The powder filling rate is 54% or less, the cracking / chip generation rate immediately after firing is 16% or more, the production yield is low, the dimensional difference rate in the XY direction is 1% or more, and the relative density is less than 99%, It turns out that a sheet | seat cannot be obtained with precise | minute and dimensional stability.

  Further, in Test Example 6 where the powder was pulverized without heat treatment, the amount of the binder was required to be as large as 18 parts by mass because of the large specific surface area of the powder, and the powder filling rate was lower than that of the production method of the present invention. This is probably the reason why cracking and chipping occur at 20% or more and the manufacturing yield is the lowest. Therefore, it can be seen that even if a thin film sheet is produced using ordinary stabilized zirconia powder, the productivity is inferior to the production method of the present invention.

  Further, from Reference Examples 1, 2, 3 and 4 in Table 2, when the thickness of the cubic zirconia sheet is 230 μm or more, firing is performed without using the cubic zirconia sheet used in the production method of the present invention. The rate of occurrence of cracks and chips immediately after that was 5% or less with little change in production yield, and the dimensional difference rate in the XY direction was 0.9% or less, indicating that there was no change in productivity.

  The thin film cubic zirconia sheet for a solid oxide fuel cell according to the present invention corresponds to a thin film demanded by the market, and in particular, a cube having a dense and excellent dimensional accuracy with a sheet thickness of 50 μm to 160 μm. An excellent method for producing a crystalline zirconia sheet is provided.

Claims (5)

A method for producing a thin film cubic zirconia sheet having a thickness of 50 μm or more and 160 μm or less for a solid oxide fuel cell,
Mixing a slurry raw material containing cubic stabilized zirconia powder, a solvent and a binder to prepare a slurry;
A step of continuously applying a tape on the polymer film by a tape casting method using the obtained slurry and drying to obtain a green tape;
A step of punching and cutting the obtained green tape into a predetermined shape to obtain a green sheet, and a step of firing the obtained green sheet;
The BET specific surface area of the zirconia powder is 3 m ² / g or more and 10 m ² / g or less, and the 90 volume% diameter (D ₉₀ ) of the zirconia powder is 0.25 μm or more and 0.8 μm or less, and 50 volume% diameter. The ratio of (D ₅₀ ) to 90 volume% diameter (D ₉₀ / D ₅₀ ) is more than 1 and 2 or less, and the ratio of 90 volume% diameter (D ₉₀ ) to 100 volume% diameter (D ₁₀₀ ) (D ₁₀₀ / D ₉₀ ) is used, wherein the powder is more than 1 and 4 or less. 2. The method according to claim 1, wherein the cubic stabilized zirconia powder has a bulk density of 1.05 g / cm ³ or more and 1.3 g / cm ³ or less.   The cubic stabilized zirconia powder is composed of stabilized zirconia containing 7 to 15 mol% of an oxide of at least one element selected from the group consisting of scandium, yttrium, cerium and ytterbium as a stabilizer. The manufacturing method in any one of 1-2.   As the slurry material, a recovered green body containing cubic stabilized zirconia powder is used, and the amount of the recovered green body used is converted into the mass of the cubic stabilized zirconia powder contained in the recovered green body. The production method according to any one of claims 1 to 3, wherein the content is 5% by mass or more and 50% by mass or less in the mass of the total cubic stabilized zirconia powder contained in the slurry.   The manufacturing method according to claim 1, wherein the slurry has a solid content concentration of 70 to 90% by mass.